In some workpiece processing systems, the workpiece is disposed on a platen, which can be rotated. This platen may also include electrical components, such as electrodes that are in communication with a power source. Additionally, this platen may have fluid conduits to allow a fluid to pass therethrough to heat or cool the platen. These fluid conduits are in communication with an external fluid source and an external fluid sink. Because the platen rotates, a rotary union is typically used to link the platen to the external components. The rotary union provides the electrical connections, as well as fluid inlets and fluid outlets. In some embodiments, the electrical connections may be integrated, while in other embodiments, a separate electrical rotary union may be employed. Further, typically, one end of the rotary union is disposed in a process chamber, which is maintained at very low pressure, while the other side is disposed at atmospheric conditions.
The workpiece may be a semiconductor wafer, which is subjected to one or more processes while disposed on the platen. These processes may include etching, deposition and ion implantation.
In some particular embodiments, the platen is cooled to cold temperatures to enhance the process being performed on the workpiece. This may be achieved by passing a cold fluid through the fluid conduits in the platen. However, seals used in conventional rotary unions often fail to seal at cryogenic temperatures. For example, leakage may result from a shrinkage of the seal due to temperature changes, from the seal becoming brittle or less compliant due to the low temperatures, or due to other reasons. Consequently, the minimum workpiece temperature that can be attained may be based on the ability of the rotary union to continue functioning properly. In other embodiments where cryogenic temperatures are used, the rotary union may be replaced with stationary conduits, such that the platen is incapable of rotation.
Consequently, it would be beneficial if there was a rotary union that could withstand these extremely low temperatures without failing. Such a rotary union would make it possible to perform cryogenic processing of the workpiece using a rotating platen.